Method of increasing tensile strength of plastic materials

ABSTRACT

Plastic ropes composed of polyethylene and polypropylene strands exposed to high hydrostatic pressure materially increase in tensile strength without a corresponding increase in strand diameter.

United States Patent [191 Muraoka 1 Jan. 16, 1973 METHOD OF INCREASING TENSILE 3,9251% 77 171202 l lood .1. ..57/157 R STRENGTH 0F PLASTIC MATERIALS 3,048,963 8/1962 Himmelfarb et a1. ..57/l57 R ['75] Inventor: James S. Muraoka, Oxnard,'Calif. OTHER PUBLICATIONS 93030 .i H [73] Assignee: The United States of America as :2 1 tg if: g i g ggi s i E g g f by the secretary of the Dec. 1965, pages 815, 817, 818, 821 relied on. [22] Fied: Iii-Rh 18 1971 Primary ExaminerRobert F White Assistant Examiner-Willard E. Hoag Attorney-Richard S. Sciascia, Q. Baxter Warner and Gayward N. Mann Appl. No.: 125,827

US. Cl ,.264/88, 264/340 Int. Cl. ..B29c 23/00, B29c 25/00 [57] ABSTRACT Field of Search ..S7/l56 R, 160, 162; 264/88, Plastic ropes composed of polyethylene and References Cited UNITED STATES PATENTS 2 Claims, No Drawings Kies et al ..264/88 METHOD OF INCREASING TENSILE STRENGTH OF PLASTIC MATERIALS STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to plastic rope strands and more particularly relates to a method of increasing tensile strength of polyethylene and polypropylene rope strands.

2. Description of the Prior Art Most rope specimens when submitted to high hydrostatic pressures encountered at great ocean depths will suffer some deterioration reduction in their breaking strength. However, rope strands manufactured of certain plastic materials (polypropylene and polyethylene) contrary to expectations tend to increase in tensile strength with a corresponding enhancement of breaking strength when subjected to high hydrostatic pressures. This phenomenon is probably due to a reorientation of the molecular chain structure.

SUMMARY OF THE INVENTION Briefly, the present invention involves a rope, the strands being manufactured of polypropylene or polyethylene which has been subjected to a high hydrostatic pressure. Polypropylene and' polyethylene strands thus treated show a remarkable increase in tensile strength as compared to non-pressure treated strands.

STATEMENT OF THE OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide plastic rope strands of enhanced strength characteristics.

Another object is to provide a lightweight yet strong rope for a variety of purposes.

Another object is to provide a strong plastic rope having enhanced strength characteristics by subjecting rope strands of polypropylene or polyethylene to high hydrostatic pressure.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention comprises a rope manufactured from either polyethylene or polypropylene strands which are subjected to a hydrostatic pressure of about 10,000 psi for about 6 to 7 continuous hours. The thus treatedpolyethylene and polypropylene ropes" when tested showed an increase in tensile strength as compared to non-pressure treated rope materials.

It should be noted that although the present process is particularly adaptable to enhancing the strength of elongated rope strands of polyethylene or including considerable polypropylene, other design configurations may also be employed. For example cords, tubing rods, cubes and practically any other configuration of polyethylene or polypropylene may be treated by the present process with a resultant material increase in tensile strength.

For confirmation purposes, six 2-foot' long test specimens were cut from a roll of continuous length rope having strands of both polyethylene and polypropylene. Three each of these ropes were placed inside a nine-inch diameter pressure-vessel filled with water and 10,000 psi of hydrostatic pressure was applied for 6.5 continuous hours. The results of a tensile strength test on these ropes as compared to non-pressure treated ropes is shown in Table I.

TABLE I Breaking Strength of Rope Specimens Before and After Exposure to 10,000 psi Hydrostatic Pressure Breaking Strength (lbs) Rope Specimen Non-Pressure Treated Pressure Change Control Treated PolypropyleneStrands 1 17 5 l300 PolypropyleneStrarids 1175 l3l2 8.8% Polypropylene Strands 1175 I225 83min strength 1175 (avg) l279(avg) RQ XQFDYIQAQSLQQ, .&Li W H00 Polyethylene Strands 937 l 170 l 1% Polyethylene Strands 1175 H gain in strength 1025 (avg) ll50(avg) Table II which follows dramatically compares the breaking strength of cotton, manilla and nylon rope specimens in a dry condition both before and after high hydrostatic pressure exposure. The tests show that cotton and manila rope specimens lost about 47 percent and 46 percent of their original strength. Nylon rope had lost about 29 percent of its strength.

TABLE II Breaking Strength of Rope Specimens Before and After 4,640 psi Hydrostatic Pressure Exposure Maintained Nylon 1437 g l I37 Light 1 slime rowth',

1652 I040 29 loss in strength I544 (avg) 1092 (avg) Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

lclaim:

l. A method for increasing the tensile strength of plastic material selected from the group consisting of polyethylene and polypropylene, said method comprising: placing a lengthof said material in a pressure vessel, filling said vessel with water and applying hydrostatic pressure of about 10,000 psi for not less than six hours nor more than seven hours.

2. The method of claim 1 wherein said material is in the form of a rope. 

2. The method of claim 1 wherein said material is in the form of a rope. 